Syntheses, Raman Spectroscopy and Crystal Structures of Alkali Hexa-fluoridorhenates(IV) Revisited

The A2[ReF6] (A = K, Rb and Cs) salts are isotypic and crystallize in the trigonal space group type P\overline{3}m1, adopting the K2[GeF6] structure type. Common to all A2[ReF6] structures are slightly distorted octa­hedral [ReF6]2− anions with an average Re—F bond length of 1.951 (8) Å. In those salts, symmetry lowering on the local [ReF6]2− anions from Oh (free anion) to D3d (solid-state structure) occur. The distortions of the [ReF6]2− anions, as observed in their Raman spectra, are correlated to the size of the counter-cations

Fluorido-Komplexe von Technetium

Summary of contents Abbreviations ix Abstract xi Chapter 1. Introduction 1 1.1. Introduction 8 1.2. Background considerations 8 1.3. Goal of the present research 11 1.4. References 11 Chapter 2. Fluoridonitridotechnetate(VI) complexes 7 2.1. Introduction 8 2.2. Attempted ligand exchange reaction 8 2.3. Synthesis from nitridotechnetic(VI) acid 11 2.4. Synthesis from pertechnetate 22 2.5. Reactions of [TcNF4]- 27 2.6. References 27 Chapter 3. Hexafluoridotechnetate(IV) 31 3.1. Introduction 32 3.2. Synthesis by metathesis reaction 33 3.3. Synthesis from pertechnetate 34 3.4. Hydrolysis of [TcF6]2- 42 3.5. Reactions of M2[TcF6] salts 47 3.6. Reactions of [TcF6]2- with Lewis acids 47 3.7. References 27 Chapter 4. Fluoridonitriosyltechnetium complexes 55 4.1. Introduction 56 4.2. Synthesis of [Tc(NO)(NH3)4F]4[TcF6][HF2]2 57 4.3. Synthesis of M2[Tc(NO)F5]•H2O (M = K, Rb, Cs) 64 4.4. Synthesis of [Tc(NO)(NH3)4F]X•1/2 MF (X= HF2 or PF6; MF= RbF, CsF, KPF6) 74 4.5. Synthesis of [Tc(NO)(py)4F]PF6 79 4.6. Synthesis of [Tc(NO)(NH3)4(OOCCF3)](OOCCF3)•CF3COOH 84 4.7. References 27 Chapter 5. Experimental section 93 5.1. Starting materials 95 5.2. Analytical methods 96 5.3. Syntheses 96 5.4. Crystal structure determinations 109 5.5. References 27 Summary 111 Zusammenfassung 115 Appendix Crystallographic data 119Summary This thesis describes the synthesis and characterization of novel fluorido complexes of technetium with the metal in the oxidation states of “+1”, “+2”, “+4” and “+6”. The first chapter reports about the isolation of fluoridonitridotechnetate(VI) salts either from nitridotechnetic(VI) acid or directly from pertechnetate by the use of additional reducing agents. The cesium salt of the compound forms a dimeric oxido-bridged complex, whereas the tetraethylammonium salt forms a tetrameric oxido-bridged complex. Both the dimeric and the tetrameric oxido-bridged complexes re-form the monomeric [TcNF4]- in solution. This could be identified by EPR spectroscopy. In the second chapter, syntheses, structural chemistry and reactivity of hexafluoridotechnetate(IV) salts are reported. Hitherto, the known synthetic routes for the preparation of hexafluoridotechnetate(IV) were either tedious or time-consuming. This thesis contains novel and improved syntheses for [TcF6]2- salts. The products are colorless and have been identified for the first time by single-crystal X-ray analysis of the ammonium, sodium, potassium, rubidium, cesium and tetramethylammonium salts. The work in this thesis explains the origin of the pink color of [TcF6]2-, which has been reported in the literature before. This color is exclusively due to the initial hydrolysis product of the compound. In alkaline media, a slow hydrolysis of [TcF6]2- is observed and the first step hydrolysis product, the dimeric oxido-bridged complex [F5Tc–O–TcF5]4-, could be isolated and studied structurally. The attempted synthesis of the binary fluoride TcF4 from hexafluoridotechnetate(IV), SbF5 and aHF resulted in the formation of a yellow tan solid. The third chapter of this thesis reports the synthesis and characterization of fluoridonitrosyltechnetium compounds with the metal in the oxidation states “+2” and “+1” by using acetohydroxamic acid as reducing agent. The reduction of hexafluoridotechnetate(IV) by acetohydroxamic acid under aqueous acidic conditions at room temperature gives the technetium(I) cation [Tc(NO)(NH3)4F]+ as [TcF6]2-/(HF2)- salt directly from the reaction mixture. This compound represents the first nitrosyltechnetium complex with a fluorido ligand. The source for the nitrosyl/ammine ligands is the hydroxamic acid. The oxidation state of the metal in [Tc(NO)(NH3)4F]+ was confirmed by 99Tc and 19F NMR spectroscopy. Reactions of pertechnetate with acetohydroxamic acid in the presence of conc. HF(aq) result in the formation of mixtures of two products: pentafluoridonitrosyltechnetate(II) and the Tc(I) nitrosyl complex, [Tc(NO)(NH3)4F]+. The compounds were characterized by IR, Raman, EPR, NMR spectroscopy and their structures were confirmed by single crystal X-ray analysis. [Tc(NO)F5]2-reacts with pyridine under formation of the Tc(I) pyridine complex, [Tc(NO)(py)4F]+. The compound was characterized by IR, 99Tc, 19F NMR spectroscopy and single crystal structure analysis. The second product, the Tc(I) nitrosyl complex [Tc(NO)(NH3)4F]+ was isolated as (HF2)- or PF6- salts. It was characterized by IR, Raman, 99Tc and 19F NMR spectroscopy. The crystal structure confirms the moiety of the complex to be similar to that of “Eakin’s pink complex”, [Tc(NO)(NH3)(OH2)]Cl2. During the reaction with trifluoroacetic acid, the fluorido ligand of [Tc(NO)(NH3)4F] is replaced by the trifluoroacetato ligand. The resulting compound is crystallized as trifluoridoacetate. It was characterized by IR, 99Tc, 19F NMR spectroscopy and single crystal X-ray diffraction.Zusammenfassung Diese Dissertationsschrift befasst sich mit der Synthese und Charakterisierung neuer Technetiumfluoride mit dem Metall in den Oxidationsstufen “+1”, “+2”, “+4” und “+6”. Im ersten Kapitel wird über die Isolierung von unterschiedlichen Salzen von Fluoridonitridotechnetaten(VI) entweder aus Nitridotechnetium(VI)-säure oder aus Pertechnetat durch den Einsatz geeigneter Reduktionsmittel berichtet. Das Cäsiumsalz dieser Verbindung bildet einen oxido-verbrückten, dimeren Komplex, während das Tetraethylammoniumsalz einen tetrameren Komplex bildet. Beide Salze dissoziieren in HF-Lösung und bilden [TcNF4]-. Dies konnte durch EPR Spektroskopie nachgewiesen werden. Im zweiten Kapitel wird über Synthese, Struktur und Reaktivität von Hexafluoridotechnetat(IV) berichtet. Die wenigen, bisher bekannten Syntheserouten für Hexafluoridotechnetat(IV)- Salze sind entweder präparativ aufwändig oder zeitaufwändig. Diese Arbeit beschreibt ein Reihe neuer und verbesserter Synthesen für [TcF6]2- und dessen Salze. Die Natrium-, Kalium-, Rubidium-, Cäsium- und Tetramethylammoniumsalze dieser Verbindung wurden als farblose Kristalle isoliert und durch Röntgenkristallstrukturanalyse charakterisiert. Der Ursprung für die in der Literatur beschriebene rosa Farbe von [TcF6]2- wurde untersucht. Diese Farbe kommt durch ein Hydrolyseprodukt von [TcF6]2- zustande. Im alkalischen Medium wird eine langsame Hydrolyse von [TcF6]2- beobachtet und das erste Hydrolyseprodukt, [F5Tc-O-TcF5]4-, konnte kristallin isoliert und strukturell charakterisiert werden. Die Synthese des binären Fluorids TcF4 aus Hexafluoridotechnetetat(IV) mit SbF5 in aHF führte zur Bildung eines hellgelben Niederschlags. Im dritten Kapitel dieser Arbeit wird die Synthese von Fluoridonitrosylverbindungen mit dem Metal in den Oxidationstufen “+2” und “+1” mit Acetohydroxamsäure als NO-Lieferant und Reduktionsmittel beschrieben. Die Reduktion von Hexafluoridotechnetat(IV) durch Acetohydroxamsäure in wässriger HF führt bei Raumtemperatur zur Bildung des Technetium(I)-Kations [Tc(NO)(NH3)4F]+, das als [TcF6]2-/(HF2)- Salz direkt aus der Reaktionsmischung kristallisiert wurden. Diese Verbindung ist der erste Nitrosyltechnetiumkomplex mit einem Fluoridoliganden. Die Quelle für die Nitrosyl- und Amminliganden ist die Acetohydroxamsäure. Die Oxidationsstufe des Metals in [Tc(NO)(NH3)4F]+ wurde durch 99Tc- und 19F NMR-Spektroskopie bestätigt. Die Reaktion von Pertechnetat mit Acetohydroxamsäure in konz. HF(aq) (48%) ergab eine Mischung aus zwei Produkten: Pentafluoridonitrosyltechnetat(II) und [Tc(NO)(NH3)4F]+. Die Verbindungen wurden durch IR-, Raman-, EPR- und NMR-Spektroskopie charakterisiert und ihre Strukturen wurden durch Röntgenstrukturanalyse bestätigt. Das zweite Produkt, [Tc(NO)(NH3)4F]+, wurde als Salz von (HF2)- oder PF6- isoliert und durch IR-, Raman-, 99Tc-NMR und 19F-NMR-Spektroskopie charakterisiert. Beider Reaktion von [Tc(NO)(NH3)4F]+ mit Trifluoressigsäure wird der Fluoridoligand durch einen Trifluoracetatoliganden ersetzt. Das Produkt kristallisiert als Trifluoracetat und wurde durch IR, 99Tc-NMR- und 19F-NMR-Spektroskopie und Röntgenstrukturanalyse charakterisiert

Bis(tetra­phenyl­arsonium) Hexa­fluorido­technetate(IV) Dihydrate: Preparation, Structure and Spectroscopic Analysis

Reports of quadrivalent transition-metal fluoride salts containing bulky organic cations are limited. In this context, we prepared the bis­(tetra­phenyl­arsonium) hexa­fluorido­technetate(IV) dihydrate salt, (C24H20As)2[TcF6]·2H2O, by a cation metathesis reaction of (NH4)2[TcF6] in water. This is the first report of an arsonium salt of the hexa­fluorido­technetate(IV) dianion. (AsPh4)2[TcF6]·2H2O crystallizes in the triclinic space group P[\overline{1}]. The [TcF6]2− anion adopts a slightly distorted octa­hedral geometry with an average Tc—F bond length of 1.933 Å. The cyclic voltammogram of (AsPh4)2[TcF6]·2H2O in CH3CN shows a one-electron reversible oxidation wave at 1.496 V

Bis(tetraphenylarsonium) hexachloridozirconate(IV) acetonitrile tetrasolvate

The bis(tetraphenylarsonium) hexachloridozirconate(IV) salt, (AsPh4)2[ZrCl6] (Ph = C6H5), was prepared more than 25 years ago [Esmadi & Sutcliffe (1991). Indian J. Chem. 30 A, 99–101], but its crystal structure was never reported. By following a similar experimental procedure, the compound was synthesized and its crystal structure was investigated as a acetonitrile tetrasolvate, (As(C6H5)4)2[ZrCl6]·4CH3CN, by single-crystal X–ray diffraction. The [ZrCl6]2− anion adopts a slightly distorted octahedral coordination sphere, with Zr—Cl bond lengths of 2.4586 (6), 2.4723 (6), and 2.4818 (5) Å, and Cl—Zr—Cl angles ranging from 89.602 (19) to 90.397 (19)°

Hexafluoridotechnetate(IV) Revisited

Novel synthetic routes to hexafluoridotechnetate(IV) are reported, and for the first time the single-crystal X-ray structures of several M2[TcF6] salts (M = Na, K, Rb, Cs, NH4, and NMe4) were determined. The ammonium and the alkaline metal salts crystallize in the trigonal space group P3m, while the NMe4(+) salt belongs to the space group R3. [TcF6](2-) salts are widely stable in aqueous solution. In alkaline media, however, a slow hydrolysis is observed, and the first hydrolysis product, the dimeric, oxido-bridged complex [F5Tc-O-TcF5](4-), could be studied structurally

Expanding the Chemistry of Rhenium Metal–Metal Bonded Fluoro Complexes: Facile Preparation and Characterization of Paddlewheel Complexes

Quadruply bonded rhenium­(III) dimers with the stoichiometry Re₂L₄F₂ (<b>1</b>, L = hexahydro-2<i>H</i>-pyrimido­[1,2a]­pyrimidinate (hpp^–); <b>2</b>, L = diphenyl formamidinate (dpf^–)) were prepared from the solid-state melt reactions (SSMRs) between (NH₄)₂[Re₂F₈]·2H₂O and HL. Those compounds were characterized in the solid state by single-crystal X-ray diffraction and in solution by UV–visible spectroscopy and cyclic voltammetry. The compound [Re₂(hpp)₄F₂]­PF₆ (<b>3</b>) was prepared from the one-electron oxidation of Re₂(hpp)₄F₂ with [Cp₂Fe]­PF₆. Compounds <b>1</b>–<b>3</b> are isostructural with the corresponding chloro derivatives. In solution, compound <b>1</b> undergoes two one-electron oxidations. Comparison with its higher halogen homologues reveals that Re₂(hpp)₄F₂ (<b>1</b>) is more easily oxidized than its chloro and bromo analogues

Fluoridonitrosyl Complexes of Technetium(I) and Technetium(II). Synthesis, Characterization, Reactions, and DFT Calculations

A mixture of [Tc­(NO)­F₅]^2– and [Tc­(NO)­(NH₃)₄F]⁺ is formed during the reaction of pertechnetate with acetohydroxamic acid (Haha) in aqueous HF. The blue pentafluoridonitrosyltechnetate­(II) has been isolated in crystalline form as potassium and rubidium salts, while the orange-red ammine complex crystallizes as bifluoride or PF₆^– salts. Reactions of [Tc­(NO)­F₅]^2– salts with HCl give the corresponding [Tc­(NO)­Cl_4/5]^−/2– complexes, while reflux in neat pyridine (py) results in the formation of the technetium­(I) cation [Tc­(NO)­(py)₄F]⁺, which can be crystallized as hexafluoridophosphate. The same compound can be synthesized directly from pertechnetate, Haha, HF, and py or by a ligand-exchange procedure starting from [Tc­(NO)­(NH₃)₄F]­(HF₂). The technetium­(I) cation [Tc­(NO)­(NH₃)₄F]⁺ can be oxidized electrochemically or by the reaction with Ce­(SO₄)₂ to give the corresponding Tc­(II) compound [Tc­(NO)­(NH₃)₄F]²⁺. The fluorido ligand in [Tc­(NO)­(NH₃)₄F]⁺ can be replaced by CF₃COO^–, leaving the “[Tc­(NO)­(NH₃)₄]²⁺ core” untouched. The experimental results are confirmed by density functional theory calculations on [Tc­(NO)­F₅]^2–, [Tc­(NO)­(py)₄F]⁺, [Tc­(NO)­(NH₃)₄F]⁺, and [Tc­(NO)­(NH₃)₄F]²⁺

Octafluorodirhenate(III) Revisited: Solid-State Preparation, Characterization, and Multiconfigurational Quantum Chemical Calculations

A simple method for the high-yield preparation of (NH₄)₂[Re₂F₈]·2H₂O has been developed that involves the reaction of (<i>n</i>-Bu₄N)₂[Re₂Cl₈] with molten ammonium bifluoride (NH₄HF₂). Using this method, the new salt [NH₄]₂[Re₂F₈]·2H₂O was prepared in ∼90% yield. The product was characterized in solution by ultraviolet–visible light (UV-vis) and ¹⁹F nuclear magnetic resonance (¹⁹F NMR) spectroscopies and in the solid-state by elemental analysis, powder X-ray diffraction (XRD), and infrared (IR) spectroscopy. Multiconfigurational CASSCF/CASPT2 quantum chemical calculations were performed to investigate the molecular and electronic structure, as well as the electronic absorption spectrum of the [Re₂F₈]^2– anion. The metal–metal bonding in the Re₂⁶⁺ unit was quantified in terms of effective bond order (EBO) and compared to that of its [Re₂Cl₈]^2– and [Re₂Br₈]^2– analogues